A method to facilitate collaborative learning in complex learning environments was developed and evaluated. Sixteen college students of educational science were given the CoStructure-Tool, a task-specific computer-based tool developed on the basis of concept mapping techniques to support the processes of knowledge construction in collaborative learning. The tool includes concept cards for case information and cards for theoretical concepts, with a screen divided into empirical and theoretical planes. Sixteen other students collaborated without this support in a control condition. Students in both conditions had to work on complex cases in the domain of education. The use of the mapping tool had substantial effects on collaborative knowledge construction. Dyads in this group produced more on-task contributions and used more theoretical concepts. Use of the mapping tool also facilitated transfer of prior knowledge, but no differences were found in the use of theoretical concepts provided in the learning environment. The CoStructure-Tool proved to be a method for facilitating cooperation that was effective in supporting specific processes and in improving the transfer of prior knowledge. (Contains eight references.) (SLD)